Developments in technology have been accompanied by an increased reliance on fuel and industrial chemicals from petrochemical sources. Such fuel sources are becoming increasingly limited and difficult to acquire. With the burning of fossil fuels taking place at an unprecedented rate, it is likely that the world's demand for fuel and petrochemical derived chemicals will soon outweigh current supplies.
As a result, efforts have been directed toward harnessing sources of renewable energy, such as sunlight, water, wind, and biomass. The use of biomass to produce new sources of fuel and chemicals which are not derived from petroleum sources (e.g., biofuel) has emerged as one alternative option.
Biofuel is a biodegradable, clean-burning combustible fuel which can be comprised of alkanes and/or esters. An exemplary biofuel is biodiesel. Biodiesel can be used in most internal combustion diesel engines in either a pure form, which is referred to as “neat” biodiesel, or as a mixture in any concentration with regular petroleum diesel or other biodiesels.
Biodiesel offers a number of beneficial properties compared to petroleum-based diesel, including reduced emissions (e.g., carbon monoxide, sulphur, aromatic hydrocarbons, soot particles, etc.) during combustion. Biodiesel also maintains a balanced carbon dioxide cycle because it is based on renewable biological materials. Biodiesel is typically completely biodegradable, and has good safety profile due to its relative high flash point and low flammability. Furthermore, biodiesel provides good lubrication properties, thereby reducing wear and tear on engines.
Current methods of making biodiesel involve transesterification of triacylglycerides from vegetable oil feedstocks, such as from rapeseed in Europe, from soybean in North America, and from palm oil in South East Asia. Industrial-scale biodiesel production is thus geographically and seasonally restricted to areas where vegetable oil feedstocks are produced. The transesterification process leads to a mixture of fatty esters which can be used as biodiesel, but also to an undesirable byproduct, glycerin. To be usable as biodiesel, the fatty esters must be further purified from the heterogeneous product. This increases costs and the amount of energy required for fatty ester production and, ultimately, biodiesel production as well. Furthermore, vegetable oil feedstocks are inefficient sources of energy because they require extensive acreage for cultivation. For example, the yield of biodiesel from rapeseed is only 1300 L/hectare because only the seed oil is used for biodiesel production, and not the rest of the rapeseed biomass. Additionally, cultivating some vegetable oil feedstocks, such as rapeseed and soybean, requires frequent crop rotation to prevent nutrient depletion of the land.
PCT Publication No. WO 2007/136762 discloses recombinant microorganisms that are capable of synthesizing products derived from the fatty acid synthetic pathway, including, inter alia, fatty acid esters and fatty alcohols. In particular, certain fatty acid derivatives are described having defined carbon chain length, branching and saturation levels. The '762 publication describes recombinant cells that utilize endogenous overexpression or heterologous expression of thioesterase proteins in the production of fatty acid derivatives.
PCT Publication No. WO 2008/119082 discloses genetically engineered cells and microorganisms that produce products from the fatty acid biosynthetic pathway, including, inter alia, fatty acid esters and fatty alcohols. The '082 publication describes recombinant cells that utilize overexpression of acyl-CoA synthetase enzymes to more efficiently produce fatty acid derivatives.
U.S. Pat. No. 5,955,329 discloses genetically engineered plant acyl-ACP thioesterase proteins having altered substrate specificity. In particular, the '329 patent discloses producing engineered plant acyl-ACP thioesterases, wherein the engineered plant acyl-ACP thioesterases demonstrate altered substrate specificity with respect to the acyl-ACP substrates hydrolyzed by the plant thioesterases as compared to the native acyl-ACP thioesterase.
While the prior art discloses certain useful disclosures regarding the production of certain fatty acid derivatives, a need exists in the field for improved methods and processes for more efficient and economical production of such fatty acid derivatives, and also for technology facilitating the production of compositions that have altered product specifications. As a specific example, a need exists for the production of fatty acid compositions having pre-designed, or “tailored,” specifications and properties for particular applications such as fuels, detergents, lubricants, industrial precursor molecule and other valuable applications of fatty acid derivatives.